An LED device is known, in which an LED in a bare chip state (hereinafter, also referred to as an LED die) is mounted onto a submount substrate and which is packaged by coating with a resin or the like. The submount substrate is a small-sized substrate that is inserted between the LED die and a large-sized substrate (hereinafter, also referred to as a mother substrate) on which other electronic parts, such as resistors capacitors, are mounted, and the submount substrate is also referred to as an interposer. The submount substrate includes an anode electrode and a cathode electrode on the bottom in opposition to the surface of the mother substrate (e.g., see Patent Document 1).
FIG. 14 is a perspective view of a conventional semiconductor package corresponding to FIG. 1 of Patent Document 1, and FIG. 15 is a bottom view of a conventional semiconductor package corresponding to FIG. 4 of Patent Document 1.
An LED device (semiconductor package) 20 has a submount substrate (wire substrate) 10 and an LED die (LED element) 61 flip-chip-mounted on the submount substrate. Bumps 61a and 61b joined to the cathode electrode and the anode electrode, respectively, of the LED die are provided on the bottom of the LED die 61. The submount substrate 10 has a ceramic substrate 11 and a pair of electrodes 12 and 13 arranged on the ceramic substrate 11. Each of the pair of electrodes 12 and 13 has surface electrodes 12a and 13a, side electrodes 12b and 13b (not illustrated), and bottom electrodes 12c and 13c and those electrodes function as the anode electrode and the cathode electrode of the LED device 20. The LED die 61 is joined to land portions that are formed on the surface electrodes 12a and 13a, respectively, of the pair of electrodes 12 and 13 via the bumps 61a and 61b. 
Further, pairs of recesses 11a and 11b and vias 11c and 11d are formed in the submount substrate 10. The side electrodes 12b and 13b are arranged in the pair of recesses 11a and 11b, and the vias 11c and 11d conduct heat generated in the LED die 61 from the surface of the submount substrate to the bottom.
The bottom electrodes 12c and 13c having identical shapes and the identical areas are arranged on the bottom of the LED device 20. The size and spacing of the upper-side electrodes 12a and 12b are determined by the electrode specifications (design rules, mounting accuracy, etc.) of the LED die 61, whereas the size and spacing of the bottom electrodes 12c and 13c are determined by the mounting specifications of the mother substrate.